1. Field of Invention
The present invention is directed to an optical switch device for use in fiber optic cable communications systems. More specifically, the present invention is directed to a symmetrical matrix crossconnect apparatus used for redirecting light beams traveling in free-space in order to change routing of the fiber optic cable telecommunications network.
2. Description of Related Art
To meet the demand for communications, many telecommunications providers are building ground-based fiber optic network systems. Such a fiber optic cable telecommunications network is illustrated by way of example in FIG. 1. A plurality of switching stations S.sub.1 -S.sub.n are located throughout a service area. The switching stations S.sub.1 -S.sub.n are interconnected by a plurality of fiber optic cable trunk lines T. Because fiber optic cable is capable of carrying significantly more telecommunication signals than the antiquated copper wire systems, switching for the purpose of rerouting the fiber optic cable trunk lines remains a concern.
With reference to FIG. 1, switching station S.sub.1 is connected to two trunk lines T.sub.a and T.sub.b located in a region R.sub.1 of the service area shown in FIG. 1. Currently, trunk lines T.sub.a and T.sub.b are connected to each other by a fully-connected crossconnect and particularly by a 4.times.4 crossconnect as shown by way of example in FIG. 2. For fiber optic cables labeled link 1-4 IN from trunk line T.sub.a can be connected to any of the fiber optic cables labeled link 1-4 OUT that comprise trunk line T.sub.b. In this example, the fiber optic cable link 2 IN is connected to the fiber optic cable link 1 OUT. This fully-connected 4.times.4 crossconnect enables any fiber optic cable link 1-4 IN to be connected to any fiber optic cable link 1-4 OUT.
In order to connect any input to any output of the 4.times.4 crossconnect in FIG. 2, a free-space optical matrix crossconnect 4 is required as shown in FIG. 3. The free-space optical matrix crossconnect includes four rows and four columns of optical switch devices 6. Such optical switch devices 6 are discussed in detail in Journal of Microelectromechanical Systems, Vol. 5, No. 4, December 1996, entitled "Electrostatic Micro Torsion Mirrors for an Optical Switch Matrix" by Hiroshi Toshiyoshi and Hiroyuki Fujita. Each optical switch device 6 includes a base member 8, an actuator 10, and a reflective element 12 having a single reflective surface. The reflected element 12 is pivotally connected to the base member 8. The actuator 10 is connected to the base member 8 and the reflective element 12. Also, the actuator 10 is operative to cause the reflective elements to move to and between a reflective state and a non-reflective state. By way of example only, only two reflective elements 12 are in the reflective state as shown in column C1, row R2 and column C3, row R4. Specifically, a light beam L.sub.1 represented by a first dotted line is emitted from link 1 IN and reflected by the reflected element 12 to link 2 OUT and a light beam L.sub.2 represented by a second dotted line and is emitted from link 3 IN and is reflected by the reflective element 12 to link 4 OUT. The remaining reflective elements are in the non-reflective state which permits any light beam to travel across the free-space optical matrix crossconnect along their respective optical paths without interference. Thus, to fabricate the fully-connected 4.times.4 crossconnect, sixteen (16), i.e., 4.times.4, optical switch devices 6 are required.
An N.times.N free-space optical matrix crossconnect 14 to facilitate N number of IN links and N number of OUT links is illustrated in FIG. 4. To fabricate a fully-connected free-space optical matrix crossconnect, N.times.N optical switch devices are required. Experts in the telecommunications industry predict that within the near future large crossconnects will be required on the order of N=512. For 512.times.512 optical matrix crossconnect, 262,144 (i.e., 512.times.512) optical switch devices will be required. Fabricating a 512.times.512 fully-connected optical matrix crossconnect will be a daunting task.